Operator`s manual

OVERHAUL
MANUAL-
LYCOMING
DIRECT DRIVE
AIRCRAFT ENGINES
Section 3
General Overhaul
Procedures
age the part by overheating
and burning thin
areas ad-
jacent to the
electrodes. Again, skill
and experience
on the part of the
operator are of the
utmost import-
ance. Consult
the latest edition
of Service Instruction
No.
1285 for proper
amperage.
3-26. CORROSION-PREVENTION.
Upon completion
of
inspection,
coat all steel parts with
preservative oil.
REPAIR AND REPLACEMENT
3-27. DAMAGED
PARTS. Abnormal
damage such as
burrs, nicks, scratches,
scoring, or galling
shouldbe
removed
with a fine oil stone,
crocus cloth, or any
similar abrasive
substance. Following
any repairs of
this
type, the part shouldbe
carefully cleaned inorder
to be certain that
all abrasive has been
removed and
then checked with its
mating part to assure
that the
clearances
are not excessive. Flanged
surfaces that
are bent, warped,
or nicked may be repaired
by lap-
ping to a true surface
on a surface plate.
Again the
part should
be cleaned to be certain
that all abrasive
has
been removed. Defective
threads can sometimes
be repaired with a suitable
die or tap. Small
nicks can
be removed
satisfactorily with Swiss
pattern files or
small, edged stones,
pipe tapped threads
should not
be tapped deeper in
order to clean them up,
because
this practice
will invariably result
in an oversized
tapped
hole. If scratches
or galling are removed
from
a bearing
surface of a journal
it should be buffed to
a
high finish.
Generally it is impossible
to repair cracks;
however,
welding operations
may be performed
in
some parts of housings,
providing the area
is not a
stressed section
of the part. For example,
almost any
area of a rocker
box may be welded, but
no part of the
cylinder
head except the
fins may be welded.
3-28.
PAINTED PARTS.
Parts requiring use of
paint
for protection
or appearance
should be painted in ac-
cordance with the following
recommendations
using
material
from the following
list of approved materials.
Thinner - Toluene
or equivalent (AMS3180
or equiva-
lent Federal
Spec. TT-T-548).
Primer - Zinc chro-
mate (AMS3110
or equivalent MIL-P-8585).
Enamel -
Phthalate resin
type (AMS3125C or equivalent
MIL-
E-7729).
NOTE
All machined bosses should be masked
before painting. Do not paint areas under
hold down nuts
where torque
is required.
3-29. Aluminum
and Steel Parts. Parts
shall be clean-
ed and
degreased prior to painting.
Apply one coat sinc
chromate
primer,
thinned with
approximately
two
parts
toluene,
and air dry. Apply
one coat of enamel
and
bake at
250°F, to 300°F, for
one-half hour. Enamel
may be allowed to air
dry but an inferior
finish will
result. Parts
from which paint has
not been removed
may be
repainted
omitting
the primer
coat.
3-30.
Magnesium
Parts.
Magnesium
parts should
be
cleaned thoroughly
with a dichromate treatment
prior
to painting.
This
treatment
consists
of cleaning
all
traces of oil
and grease from the
part by using a neu-
tral, non-corrosive
degreasing
medium followed
by
a
rinse. After which
the part is immersed
for 45 min-
utes in a hot
dichromate
solution
(3/4 lb. of
sodium
dichromateto
one gallon
of water at
180°F. to
200°F.,
quantity
as required). The part
should be thenwashed
thoroughly
in cold
running water,
dipped
in hot water
and
dried in an air blast.
Immediately thereafter
the
part should
be painted with
a prime coat and engine
enamel in the
same manner as prescribed
for alumi-
num parts.
3-31. ShroudTubes.
Shroudtubes shouldbethoroughly
cleaned and
dipped in zinc chromate
primer thinned to
spraying consistency.
After the primer
is dried the
shroud tube should be
painted on the outside
with en-
gine enamel.
3-32. All
paint applied in the
foregoing operations
should preferably
be sprayed; however,
if it is neces-
saryto use a brush,
care should be exercised
to avoid
an accumulation
of
pockets of paint.
3-33. REPLACEMENT
OF STUDS. Any
studs which
are bent, broken,
damaged or loose, must
be replaced.
The method of removing
studs depends on
the type of
stud
and manner in which
it is broken. The procedure
for removing
and replacing studs
is as follows:
a. If there
is sufficient thread
area available on
stud,
use a collet grip
tool consisting of a tapered
collet
that threads onto stud
and a housing that slips
over the collet.
Tighten bolt on top
of the housing and
draw collet into
housing to lock puller
on the stud with
a tight
grip.
b. If the
collet type
tool cannot
be used,
drill a
small
hole into the stud. Employ
a pilot bushing
to
guide drill into center
of stud when stud is
broken be-
neath
the surface of the
crankcase. Redrill the
hole
to enlarge it to accomodate
the proper
size extractor.
Using the extractor,
remove the
stud.
c. After studs
have been removed,
check for size
and condition of threads in stud holes to determine
whether oversize
studs must be used
for replacement.
Coat
threads of studs withthread
lubricant, Specifica-
tion JAN-A-669,
and drive
stud to correct depth
by
using a suitable stud driver.
3-34. CORROSION-PREVENTION.
At
the conclusion
of all repair operations
and subsequent
inspection,
coat
all steel parts
with preservative
oil.
REASSEMBLY
3-35. CORROSION-PREVENTION.
Prior to assembly
of subassemblies,
all parts should
be cleaned to re-
move
all traces of preservative
oil and accumulated
foreign matter. During assembly, cover all steel parts
with a heavy
coat of preservative
oil. This mixture
should be used on all machined surfaces, especially
on bearing surfaces,
cylinder bores and piston
rings.
The practice of using plain lubricating oil during as-
sembly is not recommended.
3-36. PRE-LUBRICATIONOF PARTS PRIOR TO AS-
SEMBLY.
Many premature
failure of parts have
been
traced directly to improper pre-lubrication at engine
Revised October 1974
3-3